My U.S. Pat. No. 5,673,659 entitled "Lead Screw Driven Shaft Phase Control Mechanism", issued on Oct. 7, 1997 and assigned to the assignee of this invention, discloses a mechanism that provides a selective timing or phase adjusting system between a drive gear and a driven camshaft with the drive gear being coaxially mounted and axially affixed with respect to the driven camshaft for rotation together. An intermediate connecting member is coaxially mounted with respect to the drive gear and the camshaft and is capable of axial movement and angular movement with respect to either the camshaft or the drive gear when experiencing its relative axial movement. The intermediate connection and a coupling member are connected to a geared device that is selectively activated by an electric motor which produces axial movement of both the intermediate connection and the coupling member with respect to the camshaft and the drive gear to any desired axial position between predetermined first and second positions. The gearing device provides a unidirectional drive system which allows the electric control motor to drive the mechanism to provide the optimum shaft phasing and is operably connected to a sleeve that is axially affixed to the intermediate connecting member. When in operation, the gearing device moves the sleeve axially, which in turn, moves the intermediate member axially with respect to both the drive gear and the camshaft. The intermediate connection member is an axially shifting member that has helical splines that rotationally affix it to the camshaft to allow relative rotation of the camshaft with respect to the drive gear. In one embodiment, the gearing device drives the sleeve while in another embodiment the gearing device is a threaded lead screw engaging complementary threads formed on the sleeve. In a third embodiment disclosed in the patent, the gearing device is a part of a gear sprocket that has an internally threaded hub that engages complementary external threads on the sleeve.
In my U.S. Pat. No. 5,860,328 entitled "SHAFT PHASE CONTROL MECHANISM WITH AN AXIALLY SHIFTABLE SPLINED MEMBER", which issued Jan. 19, 1999 and assigned to the assignee of this invention, I disclose a two part variable valve timing system. In my co-pending patent application, Ser. No. 09/283,019, entitled "TWO PART VARIABLE VALVE TIMING MECHANISM", filed on Apr. 1, 1999 and assigned to the assignee of this invention, I disclose a new form of power transmission that is substituted for the threaded jackscrew system which executes the axial motion of the shifting sleeve. Inasmuch as the lowest possible friction level is desired in phase changing devices to minimize wear and to allow use of a small electric motor for varying the position of the camshaft, it is important to have a transmission arrangement with less friction than an ACME screw. As stated in the aforementioned patent application, the optimum replacement for an ACME screw would be the ball-nut recirculating screw device which enjoys very low friction in operation. However, irrespective of the many advantages provided by such a device, using it for phase changing device is not possible from a practical standpoint because the required ball-return duct would interfere with the drive gear. Accordingly, in the mechanism covered by the above patent application, I have incorporated into the phase changing device one of the ball-nut transmissions disclosed in my co-pending patent application, Ser. No. 09/271,229, entitled "BALL-NUT TRANSMISSION", filed on Mar. 17, 1999, and assigned to the assignee of this invention.